U.S. patent application number 10/866689 was filed with the patent office on 2005-06-30 for stock solution for production of nonlinear-optical materials, nonlinear-optical material, and nonlinear-optical device.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Nishikata, Yasunari, Takada, Hokuto, Uesaka, Tomozumi, Yamaguchi, Yasuhiro.
Application Number | 20050139813 10/866689 |
Document ID | / |
Family ID | 34697574 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139813 |
Kind Code |
A1 |
Yamaguchi, Yasuhiro ; et
al. |
June 30, 2005 |
Stock solution for production of nonlinear-optical materials,
nonlinear-optical material, and nonlinear-optical device
Abstract
The present invention provides stock solutions for production of
nonlinear-optical materials using a wet coating method. In
particular, the invention provides a stock solution containing a
nonlinear-optically active organic compound, which is a push-pull
.pi.-conjugated compound having a particular chemical structure,
having one or more cross-linkable functional groups. In addition,
the invention provides a stock solution comprising a
nonlinear-optically active organic compound having at least a
certain chemical structure and a matrix-forming compound having one
or more cross-linkable functional groups. Further, the invention
provides a nonlinear-optical material and a nonlinear-optical
device, both prepared by using the stock solutions.
Inventors: |
Yamaguchi, Yasuhiro;
(Minamiashigara-shi, JP) ; Uesaka, Tomozumi;
(Minamiashigara-shi, JP) ; Takada, Hokuto;
(Minamiashigara-shi, JP) ; Nishikata, Yasunari;
(Minamiashigara-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Minato-ku
JP
|
Family ID: |
34697574 |
Appl. No.: |
10/866689 |
Filed: |
June 15, 2004 |
Current U.S.
Class: |
252/582 |
Current CPC
Class: |
G02F 1/3611 20130101;
G02F 1/3616 20130101; G02F 1/3617 20130101 |
Class at
Publication: |
252/582 |
International
Class: |
F21V 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2003 |
JP |
2003-429569 |
Claims
What is claimed is:
1. A stock solution for production of nonlinear-optical materials
using a wet coating method, comprising a nonlinear-optically active
organic compound satisfying either condition (i) or (ii): (i) the
nonlinear-optically active organic compound further comprising at
least one cross-linkable functional group; and the
nonlinear-optically active organic compound is a push-pull
.pi.-conjugated compound represented by Formula (1), or (ii) the
stock solution further comprises a matrix-forming compound having
at least one cross-linkable functional group; and the
nonlinear-optically active organic compound is represented by
Formula (2): 19wherein in Formula (1), Z.sup.1 to Z.sup.3 each are
independently an aromatic group which may have substituents; L is a
.pi.-conjugated group which may have substituents; A is an
electron-withdrawing group which may have substituents; and m is 0
or 1, wherein Z.sup.1 to Z.sup.3, L and A each may be linked with
any other group to form a ring structure; and at least one of
Z.sup.1 to Z.sup.3, L and A has one or more cross-linkable
functional groups: 20wherein in Formula (2), Z.sup.4 to Z.sup.6
each are independently an aromatic group which may have
substituents; D is a .pi.-conjugated group which may have
substituents; E is an electron-withdrawing group which may have
substituents; n is 0 or 1; and Z.sup.4 to Z.sup.6, D, and E each
may be linked with any other group to form a ring structure and may
have one or more cross-linkable functional groups.
2. A stock solution according to claim 1, satisfying condition
(i).
3. A stock solution according to claim 2, wherein A in Formula (1)
represents a .pi.-conjugated electron-withdrawing group, which
contains a ring structure and may have substituents.
4. A stock solution according to claim 2, wherein a
.pi.-conjugation system that spans both ends of the Z.sup.3-L.sub.m
structure in Formula (1) is formed from five or more consecutive
unsaturated bonds.
5. A stock solution according to claim 2, wherein the
cross-linkable functional group comprises a hydrolysable silyl
group.
6. A stock solution according to claim 5, wherein a solution
containing the nonlinear-optically active organic compound is
subjected at least to a hydrolysis treatment wherein the
hydrolysable silyl group is brought into contact with a solid
catalyst and hydrolyzed, and to a catalyst-separation treatment
wherein the solid catalyst is removed from the solution after the
hydrolysis treatment.
7. A stock solution according to claim 1, satisfying condition
(ii).
8. A stock solution according to claim 7, wherein E in Formula (2)
is a .pi.-conjugated electron-withdrawing group, which has a ring
structure and may have substituents.
9. A stock solution according to claim 7, wherein a ir-conjugation
system that spans both ends of the Z.sup.6-D.sub.n structure in
Formula (2) is formed from five or more consecutive unsaturated
bonds.
10. A stock solution according to claim 7, wherein the
cross-linkable functional group comprises a hydrolysable silyl
group.
11. A stock solution according to claim 10, wherein a solution
containing the nonlinear-optically active organic compound and the
matrix-forming compound is subjected at least to a hydrolysis
treatment wherein the hydrolysable silyl group is brought into
contact with a solid catalyst and hydrolyzed, and to a
catalyst-separation treatment wherein the solid catalyst is removed
from the solution after the hydrolysis treatment.
12. A stock solution according claim 10, wherein the matrix-forming
compound comprises two or more hydrolysable silyl groups as the
cross-linkable functional groups.
13. A nonlinear-optical material prepared using a wet coating
method, wherein a stock solution for production of
nonlinear-optical materials comprising a nonlinear-optically active
organic compound is used, the stock solution satisfying the
following condition (i) or (ii): (i) the nonlinear-optically active
organic compound further comprises at least one cross-linkable
functional group; and the nonlinear-optically active organic
compound is a push-pull .pi.-conjugated compound represented by
Formula (1), or (ii) the stock solution further comprises a
matrix-forming compound having at least one cross-linkable
functional group; and the nonlinear-optically active organic
compound is represented by Formula (2): 21wherein in Formula (1),
Z.sup.1 to Z.sup.3 each are independently an aromatic group which
may have substituents; L is a .pi.-conjugated group which may have
substituents; A is an electron-withdrawing group which may have
substituents; m is 0 or 1; Z.sup.1 to Z.sup.3, L and A each may be
linked with any other group to form a ring structure; and at least
one group thereof has one or more cross-linkable functional groups:
22wherein in Formula (2), Z.sup.4 to Z.sup.6 each are independently
an aromatic group which may have substituents; D is a ir-conjugated
group which may have substituents; E is an electron-withdrawing
group which may have substituents; n is 0 or 1; and Z.sup.4 to
Z.sup.6, D, and E each may be linked with any other group to form a
ring structure and may have one or more cross-linkable functional
groups.
14. A material according to claim 13, prepared by using a stock
solution satisfying condition (i).
15. A material according to claim 13, prepared by using a stock
solution satisfying condition (ii).
16. A nonlinear-optical device prepared using a wet coating method
wherein a stock solution for production of nonlinear-optical
materials comprising a nonlinear-optically active organic compound
is used, the stock solution satisfying the following condition (i)
or (ii): (i) the nonlinear-optically active organic compound
further comprises at least one cross-linkable functional group; and
the nonlinear-optically active organic compound is a push-pull
.pi.-conjugated compound represented by Formula (1), or (ii) the
stock solution further comprises a matrix-forming compound having
at least one cross-linkable functional group; and the
nonlinear-optically active organic compound is represented by
Formula (2): 23wherein in Formula (1), Z.sup.1 to Z.sup.3 each are
independently an aromatic group which may have substituents; L is a
.pi.-conjugated group which may have substituents; and A is an
electron-withdrawing group which may have substituents; m is 0 or
1; wherein Z.sup.1 to Z.sup.3, L and A each may be linked with any
other group to form a ring structure; and at least one group
thereof has one or more cross-linkable functional groups: 24wherein
in Formula (2), Z.sup.4 to Z.sup.6 each are independently an
aromatic group which may have substituents; D is a .pi.-conjugated
group which may have substituents; E is an electron-withdrawing
group which may have substituents; n is 0 or 1; and Z.sup.4 to
Z.sup.6, D, and E each may be linked with any other group to form a
ring structure and may have one or more cross-linkable functional
groups.
17. A device according to claim 16, prepared by using a stock
solution satisfying condition (i).
18. A device according to claim 17, having a waveguide structure
comprising one or more core layers which are sandwiched by cladding
layers.
19. A device according to claim 16, prepared by using a stock
solution satisfying condition (ii).
20. A device according to claim 19, having a waveguide structure
comprising one or more core layers which are sandwiched by cladding
layers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of and priority to Japanese
Patent Application No. 2003-429569, which is incorporated herein by
reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a nonlinear-optical
material and a nonlinear-optical device applicable to fields such
as optical communication, optical wiring, optical information
processing, sensors, and image processing, and a stock solution for
producing the same.
[0004] More specifically, the invention relates to a
nonlinear-optical device such as an optical switching device,
optical modulating device, wavelength-converting device, or
phase-shifting devices utilizing second-order nonlinear-optical
effects, or a memory device or image-processing device utilizing
photorefractive effects; and a nonlinear-optical material
applicable to these applications; and a stock solution for
manufacturing the same.
[0005] 2. Description of the Related Art
[0006] Most of the functional devices important in optical fields
are realized by the use of nonlinear-optical materials, in
particular, second-order nonlinear-optical materials. Such devices
include wavelength-converting devices, optical modulating devices,
and optical switching devices, and these are important in optical
fields such as optical communication, optical wiring, optical
information processing, sensors, and image processing. Inorganic
nonlinear-optical materials, such as lithium niobate, and potassium
dihydrogen phosphate, have already been commercialized and are
widely used as second-order nonlinear-optical materials, but
recently, organic nonlinear-optical materials have been attracting
attention due to advantages in their improved nonlinear-optical
characteristics, lower material and production cost, higher
productivity and the like. Extensive research and development is
currently directed to commercialization of these materials in order
to replace conventional inorganic materials.
[0007] An essential requirement in order to achieve the
second-order nonlinear-optical effect is that there be, in
principle, no center of symmetry in the system. Second-order
nonlinear-optical materials are roughly classified into two
systems, the first being a system where an organic compound
exhibiting nonlinear-optical activity is crystallized in a crystal
structure having no symmetry center (hereinafter, referred to as a
"crystalline system"). The second system involves an organic
compound exhibiting nonlinear-optical activity (i.e., a
nonlinear-optically active organic compound) dispersed in a polymer
binder and the symmetry center of the system is eliminated by
orientation using a certain means (hereinafter, referred to as a
"dispersion system").
[0008] Although organic nonlinear-optical materials of the
crystalline system are known to exhibit extremely superior
nonlinear-optical characteristics, it is almost impossible to
control the crystal structure artificially, and thus it is very
rare that crystal structures without any symmetry centers are
obtained. Even if obtained, it is difficult to produce the large
organic crystals required for producing optical devices. In
addition, these optical materials often cause various problems, as
the organic crystals are very fragile or brittle and are often
damaged during production of the devices.
[0009] In contrast, organic nonlinear-optical materials of the
dispersion system are regarded as more promising, because they have
greater potential for commercialization. This is due to the fact
that they are provided with favorable characteristics such as good
coatability and mechanical strength, attributes that are useful for
producing devices with polymer binders.
[0010] Dispersion-type organic nonlinear-optical materials must be
optically homogeneous and transparent, and thus, the
nonlinear-optically active organic compound contained therein
should be dispersed in the polymer binder uniformly without
aggregation. In addition, as described above, it is necessary to
orient the nonlinear-optically active organic compound by using a
certain means in order to cause the anisotropy required for the
second-order nonlinear-optical effect. It is also necessary order
to obtain effective use of the functional devices and to preserve
the oriented state consistently in hot or humid environments during
production, operation, and storage of the resulting devices.
[0011] Accordingly, the nonlinear-optically active organic
compounds to be used in dispersion-type organic nonlinear-optical
materials must not only have superior nonlinear-optical
characteristics, but also a lower tendency toward aggregation and
higher compatibility with the polymer binder. The dispersion-type
organic nonlinear-optical materials are generally converted to
various devices in the form of thin films, and wet coating methods
are favorably used for forming the thin films. For this reason,
nonlinear-optically active organic compounds used in
dispersion-type organic nonlinear-optical materials should be
highly soluble in the stock solution solvents. It is also necessary
for the polymer binders to have, in addition to qualities such as
superior coatability and mechanical strength, a high
glass-transition temperature in order to consistently maintain the
orientation of the nonlinear-optically active organic compound
contained therein.
[0012] It is necessary to orient the nonlinear-optically active
organic compound as described above for generating the second-order
nonlinear-optical activity in dispersion-type organic
nonlinear-optical materials, and the electric field-poling method
is commonly used as the orientation method. The electric
field-poling method is an orientation method of applying an
electric field to a nonlinear-optical material and orienting the
nonlinear-optically active compound therein in the direction of the
applied electric field by the Coulomb force between the dipole
moment of the nonlinear-optically active compound and the applied
electric field. The orientation of the nonlinear-optically active
compound is generally assisted by the activation of molecular
motion by heating to a temperature close to the glass-transition
temperature during application of the electric field.
[0013] It is known that so-called push-pull .pi.-conjugated
compounds having an electron-donating group at one end of the
.pi.-conjugated chain and an electron-withdrawing group at the
other end are effective nonlinear-optically active organic
compounds. For example, Disperse Red 1 (generally, abbreviated to
DR1) having an N-ethyl-N-(2-hydroxyethyl)amino group as the
electron-donating group at the 4 position and a nitro group as the
electron-withdrawing group at the 4' position of the azo benzene
structure (.pi.-conjugated chain) is widely known as a typical
nonlinear-optically active organic compound. However, given that
DR1 does not in essence possess superior nonlinear-optical
characteristics and has both a lower compatibility with ordinary
polymer binders and a higher tendency to sublimate, DR1 is
problematic in that it disappears with the application of heat in
the drying and electric-field poling processes, and dialkylamino
groups tend to oxidize and deteriorate.
[0014] Various nonlinear-optically active organic compounds have
been developed hitherto to solve these problems, but compounds
satisfying all of the required characteristics at the same time
have yet to discovered. In particular, it is quite difficult to
provide a compound superior having both nonlinear-optical
characteristics and higher binder compatibility. Namely, the
nonlinear-optical characteristics of push-pull .pi.-conjugated
compounds are known to be improved by generally elongating the
.pi.-conjugated chain therein and strengthening the
electron-withdrawing capacity of electron-withdrawing group and the
electron-donating capacity of electron-donating group. Nonetheless,
the improvement in nonlinear-optical characteristics is accompanied
by an increase in aggregation between molecules, consequently
leading to a decrease in the compatibility of the conjugated
compounds with the polymer binder.
[0015] For example, it has been disclosed that a compound having
the structure shown below exhibited extremely superior
nonlinear-optical characteristics, however, it is very difficult to
produce a film where the compound is uniformly dispersed in the
polymer binder and crystal precipitation is suppressed due to its
extremely high tendency to coagulate (see e.g., Chemistry of
Materials, 2001, Vol. 13, pp. 3043 to 3050). It has been also
disclosed therein that it is necessary to use a halogenated solvent
having a low boiling point as the coating solvent, but the use of
such a halogenated solvent is not favorable as it negatively
affects air quality. 1
[0016] On the other hand, although polymethyl methacrylate
(generally abbreviated to PMMA) has been most intensively studied
as the polymer binder, the glass-transition temperature of PMMA is
lower at about 100.degree. C., and thus the orientation of a
dispersion-type organic nonlinear-optical material in the PMMA
polymer binder gradually slackens even at room temperature.
Nonlinear-optical materials derived therefrom exhibit a marked
decrease in nonlinear-optical characteristics over time. Thus,
PMMA-based optical materials are not suitable for actual use in
functional devices (e.g., Chemical Reviews, 1994, Vol. 94, No. 1,
pp. 31 to 75).
[0017] In order to solve these problems, binder polymers for
replacing PMMA have been intensively studied, leading to polymers
having glass-transition temperatures that are higher than that of
PMMA. Examples of reported binder polymers include polycarbonate,
polyimide, polysulfone, and polycyclic olefin (see e.g., Japanese
Patent Application Laid-Open (JP-A) No. 6-202177). Use of these
polymer binders having higher glass-transition temperatures is
inevitably accompanied with an increase in the heating temperature
required for electric-field poling, and this in turn causes
oxidation and disappearance by sublimation of the
nonlinear-optically active organic compounds such as DR1 during the
electric-field poling process. The compatibility between these
polymer binders having high glass-transition temperatures and a
nonlinear-optically active organic compound such as DR 1 is not
always high, and accordingly, addition of the nonlinear-optically
active organic compound at a higher concentration for the purpose
of improving the nonlinear-optical characteristics causes
aggregation or crystallization of the compound. Further, addition
of nonlinear-optically active organic compounds even at a lower
concentration, still causes aggregation or crystallization by
heating or the passage of time.
[0018] As a means for solving the problems of the dispersion-type
organic nonlinear-optical materials described above, the
introduction of a nonlinear-optically active organic compound to
the main chain and/or side-chain of a polymer, i.e., conversion of
the nonlinear-optically active organic compound to a polymeric
compound, is being studied.
[0019] For example, a nonlinear-optically active polymeric compound
having the following structure where the DR1 structure is bound to
the side chain of PMMA has been developed. 2
[0020] The glass-transition temperature of this nonlinear-optically
active polymeric compound is about 165.degree. C. and higher than
the glass-transition temperature of PMMA (about 100.degree. C.). In
contrast to the fact that DR1 can be dispersed in PMMA only at a
concentration of up to 30% by mass without crystal precipitation,
the nonlinear-optically active polymeric compound, which contains
the DR1 structure at a concentration equivalent to 82% by mass,
provides a clear film without phase separation. Accordingly, the
nonlinear-optically active polymeric compound exhibits higher
nonlinear-optical characteristics and higher stability than the
dispersion-system compounds where DR1 is dispersed in PMMA.
[0021] However, even if polymerization is possible, it is difficult
to both polymerize the monomers having a bulky nonlinear-optically
active structure and control the degree of polymerization. If the
degree of polymerization is not raised sufficiently, the resulting
polymers have significantly lower mechanical strength. In addition,
insufficient control of the degree of polymerization causes a
problem in that it is difficult to produce films having a certain
consistent thickness due to fluctuation by production lot of the
viscosity of coating solutions (stock solutions). As purification
of polymers is generally difficult, residual impurities such as
polymerization catalysts may also make it more difficult to apply
an effective electric field during electric-field poling.
Therefore, introduction of a nonlinear-optically active organic
compound into the main chain and/or side-chain of a polymer is
hardly the best method.
[0022] To solve the problems associated with the aforementioned
dispersion-type organic nonlinear-optical materials, a method of
preparing a cross-linkable nonlinear-optically active organic
compound is being studied. A nonlinear-optically active organic
compound such as DR1 is introduced to the cross-linkable functional
group in the compound, and the cross-linkable nonlinear-optically
active organic compound is coated and dried, after which
electric-field poling and curing by cross-linking treatments are
conducted simultaneously (hereinafter, referred to as a "curing by
cross-linking system"). This method provides a favorable effect of
stabilizing the oriented state significantly, as it fixes the
oriented state induced by the electric-field poling by
cross-linking. In addition, since the raw material, i.e., the
cross-linkable nonlinear-optically active organic compound, is a
low-molecular weight compound, the problems concerning the
polymerization and purification of the aforementioned
nonlinear-optically active polymeric compound are reduced.
[0023] However, conventional nonlinear-optically active organic
compounds are highly aggregative, and thus even if cross-linking
and curing of organic compounds having a cross-linkable functional
group is conducted, such organic compounds tend to aggregate or
crystallize in the drying step prior to curing by cross-linking and
clear cured films cannot be obtained. These compounds are also
problematic in that a cross-linking reaction causes gelation of the
stock solution, or with pot life of the stock solution due to
precipitation, leading to deterioration in optical quality and
increase in the production cost of the resulting films.
SUMMARY OF THE INVENTION
[0024] The present invention is provided in view of the
aforementioned problems associated with conventional art.
[0025] Namely, the invention relates to a cross-linkable organic
nonlinear-optical material having a high potential of exhibiting an
excellent stability, and provides a cross-linkable stock solution
for production of nonlinear-optical materials relieved of the
problems of aggregation and crystallization and having an excellent
pot life. Further by making the most of the stock solution, the
invention provides a nonlinear-optical material and a
nonlinear-optical device having excellent nonlinear-optical
characteristics and a superior stability at a lower cost.
[0026] As a result of intensive studies to solve the problems above
concerning the nonlinear-optically active organic compounds and the
methods of curing by cross-linking, the inventors have found that
it is possible to solve the problems by using a particular
cross-linkable nonlinear-optically active organic compound. Namely,
a first aspect of the present invention is a stock solution for
production of nonlinear-optical materials using a wet coating
method, comprising a nonlinear-optically active organic compound
satisfying either condition (i) or (ii):
[0027] (i) the nonlinear-optically active organic compound further
comprising at least one cross-linkable functional group; and the
nonlinear-optically active organic compound is a push-pull
.pi.-conjugated compound represented by Formula (1), or
[0028] (ii) the stock solution further comprises a matrix-forming
compound having at least one cross-linkable functional group;
and
[0029] the nonlinear-optically active organic compound is
represented by Formula (2): 3
[0030] wherein in Formula (1), Z.sup.1 to Z.sup.3 each are
independently an aromatic group which may have substituents; L is a
.pi.-conjugated group which may have substituents; A is an
electron-withdrawing group which may have substituents; and m is 0
or 1, wherein Z.sup.1 to Z.sup.3, L and A each may be linked with
any other group to form a ring structure; and at least one of
Z.sup.1 to Z.sup.3, L and A has one or more cross-linkable
functional groups: 4
[0031] wherein in Formula (2), Z.sup.4 to Z.sup.6 each are
independently an aromatic group which may have substituents; D is a
.pi.-conjugated group which may have substituents; E is an
electron-withdrawing group which may have substituents; n is 0 or
1; and Z.sup.4 to Z.sup.6, D, and E each may be linked with any
other group to form a ring structure and may have one or more
cross-linkable functional groups.
[0032] A second aspect of the present invention is a
nonlinear-optical material prepared using a wet coating method and
the stock solution satisfying the above-described condition (i) or
(ii).
[0033] Further, a third aspect of the present invention is
nonlinear-optical device prepared using a wet coating method and
the stock solution satisfying the above-described condition (i) or
(ii).
BRIEF DESERIPTION OF THE DRAWINGS
[0034] Preferable embodiments of the present invention will be
described in detail based on the following figures.
[0035] FIG. 1 is a schematic cross-sectional view showing a
configuration of an embodiment of the nonlinear-optical device
according to the invention, a waveguide-type electro-optical
device.
[0036] FIG. 2 is a schematic cross-sectional view showing a
configuration of an embodiment of the nonlinear-optical device
according to the invention, a waveguide-type electro-optical device
(having a channel waveguide structure).
[0037] FIG. 3 is a schematic cross-sectional view showing a
configuration of an embodiment of the nonlinear-optical device
according to the invention, a waveguide-type electro-optical device
(having a ridge waveguide structure).
[0038] FIG. 4 is schematic cross-sectional view showing an
embodiment of the nonlinear-optical device according to the
invention, an optical modulator.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The present invention provides a stock solution for
production of nonlinear-optical materials, which is superior in the
processability in forming nonlinear-optical materials by wet
coating method and allows production of nonlinear-optical materials
and nonlinear-optical devices superior in nonlinear-optical
characteristics.
[0040] The invention also provides conveniently a nonlinear-optical
material superior both in nonlinear-optical characteristics and in
thermal stability due to curing by cross-linking, and a
nonlinear-optical device higher in stability and longer in
operating time at a lower cost by using the same.
[0041] Hereinafter, the invention will be described in detail with
reference to specific embodiments.
[0042] Stock Solution
[0043] The stock solutions according to the invention are
classified into two groups, a first stock solution and a second
stock solution.
[0044] The first stock solution according to the invention is a
stock solution for production of nonlinear-optical materials by wet
coating method, containing at least a nonlinear-optically active
organic compound having one or more cross-linkable functional
groups, the nonlinear-optically active organic compound further
being a push-pull .pi.-conjugated compound represented by the
following Formula (1). 5
[0045] In the formula above, Z.sup.1 to Z.sup.3 each are
independently an aromatic group which may have substituents; L is a
.pi.-conjugated group which may have substituents; A is an
electron-withdrawing group which may have substituents; and m is 0
or 1, wherein Z.sup.1 to Z.sup.3, L and A each may be linked with
any other group to form a ring structure; and at least one of
Z.sup.1 to Z.sup.3, L and A has one or more cross-linkable
functional groups.
[0046] As will be described below, the compound having the
structure represented by the Formula (1) has a great
nonlinear-optical effect. According to the invention, a stock
solution having an excellent pot life, i.e., free from gelation or
precipitation, can be obtained with the compound, and a
nonlinear-optical material excellent in nonlinear-optical
characteristics can be produced with this stock solution.
[0047] The first stock solution according to the invention contains
at least a nonlinear-optically active organic compound having one
or more cross-linkable functional groups, and the cross-linkable
functional group may be contained by at least one group of Z.sup.1
to Z.sup.3, L, and A in the compound represented by Formula (1) and
the number of cross-linkable functional groups is not particularly
limited if it is at least one.
[0048] Z.sup.1 to Z.sup.3 in the Formula (1) each are independently
an aromatic group which may have substituents, and a phenyl or
phenylene group which may have substituents is preferable from the
viewpoints of productivity and chemical stability. Having the
triarylamine structure, the compound is more resistant to
oxidation, thermal degradation, and photodegradation. Further, the
triarylamine structure suppresses intermolecular association,
improving the dispersion of the nonlinear-optically active organic
compound in the cross-link film and suppressing the aggregation and
crystallization thereof after coating. L is a 7.pi.-conjugated
group which may have substituents. A is an electron-withdrawing
group which may have substituents and preferably from the
viewpoints of chemical stability, nonlinear-optical
characteristics, and the like, a .pi.-conjugated
electron-withdrawing group, which contains a ring structure and may
have a substituent.
[0049] In the invention, Z.sup.1 to Z.sup.3, L and A each may be
linked with any other group to form a ring structure thereof. The
bulky and rigid ring structure thus formed inhibits association of
molecules and increases oxidation resistance.
[0050] In addition, the Formula (1) preferably includes a
ir-conjugation system that spans both ends of the Z.sup.3-L.sub.m
structure formed from five or more consecutive unsaturated bonds.
As described above, it is favorable to elongate the .pi.-conjugated
chain between the electron-withdrawing and electron-donating groups
in the push-pull .pi.-conjugation compounds from the viewpoint of
improving the nonlinear-optical characteristics, and thus
.pi.-conjugation systems having 5 or more consecutive conjugated
bonds provide the compound according to the invention represented
by Formula (1) with particularly favorable nonlinear-optical
characteristics.
[0051] The .pi.-conjugation system more preferably has 7 or more
conjugated bonds, and the upper limit of the number of conjugation
is about 15, from the viewpoint of ensuring the oxidation
resistance and aggregation resistance. In the invention, the
"consecutive .pi.-conjugation system" means a system wherein
unsaturated bonds are connected one by one and thus conjugated.
[0052] The cross-linkable functional group above may be any one of
the groups including groups cross-linkable as it is, groups
cross-linkable only in the presence of another group, groups
cross-linkable in the presence of a cross-linking aid, and the
like. The cross-linking bond formed may be an ionic bond, hydrogen
bond, coordination bond, or covalent bond, but a covalent bond is
preferable from the viewpoint of stability.
[0053] Typical examples of the cross-linkable functional groups
include: a hydroxy group, an amino group, a carboxyl group, an
epoxy group, an isocyanate group, substituted or unsubstituted
benzocylcobutene groups, substituted or unsubstituted vinyl groups,
substituted or unsubstituted hydroxysilyl groups, substituted or
unsubstituted hydrolysable silyl groups, and the like. Among them,
substituted or unsubstituted hydrolysable silyl groups are
particularly preferable, as they provide cross-linked and cured
films superior in optical quality, mechanical strength, solvent
resistance, chemical stability, and the like.
[0054] The hydrolysable silyl group is a silyl group of which part
or all of the hydrogen atoms are replaced with hydrolysable groups
typically by an alkoxy group. When hydrolysable silyl groups are
used as the cross-linkable functional groups, all the
cross-linkable functional groups need not be but are preferably
hydrolysable silyl groups.
[0055] Details about nonlinear-optically active organic compounds
having the hydrolysable silyl groups will be described below.
[0056] Because these cross-linkable functional groups react
gradually even at room temperature, the pot life of the stock
solution containing the groups for production of nonlinear-optical
materials is generally short, but may be extended by storing them
under a dry low-temperature condition in a dark place.
[0057] Typical examples of the nonlinear-optically active organic
compound having one or more cross-linkable functional groups,
represented by Formula (1), are as follows. 678
[0058] The present inventors have earlier found the method that
could drastically improve the pot life at room temperature and
atmospheric pressure of a stock solution for production of
nonlinear-optical materials containing a cross-linkable
nonlinear-optically active organic compound having a particularly
preferred cross-linkable functional group, i.e., a hydrolysable
silyl group (Japanese Patent Application No. 2003-77616).
[0059] To conventional stock solutions for production of
nonlinear-optical materials containing a cross-linkable
nonlinear-optically active organic compound having one or more
hydrolysable silyl groups, an acid catalyst such as hydrochloric
and sulfuric acids or a base catalyst such as pyridine or triethyl
amine is added for acceleration of hydrolysis and polycondensation
of the hydrolysable silyl group, but the practice brought the
problems in pot life, such as the gelation of solution in a shorter
period of time and the precipitation of solid matters therein, as
hydrolysis and polycondensation reactions take place at the same
time in the stock solutions which are added with such a homogeneous
catalyst.
[0060] Although it is possible to produce clear films by coating
the solution before the gelation and precipitation occur, such a
procedure is lower in operational efficiency, inevitably leading to
increase in production cost. In addition, polycondensation of the
ingredients therein, which proceeds gradually even before the
gelation and precipitation occur, raised the problems that it is
more difficult to obtain nonlinear-optical materials having a
particular film thickness due to variation in solution viscosity
and the optical quality of the films obtained deteriorates due to
generation of minute hardened particles in the solution. Further,
the acid or base catalyst remains in the film even during
electric-field poling and causes a problem of improper application
of poling electric field to the film due to its ionic
conductivity.
[0061] With respect to these conventional stock solutions for
production of nonlinear-optical materials containing a
cross-linkable nonlinear-optically active organic compound having
one or more hydrolysable silyl groups, the method found by the
inventors drastically improves the pot life of the stock solution
for production of nonlinear-optical materials containing a
cross-linkable nonlinear-optically active organic compound having
one or more hydrolysable silyl groups without sacrificing the
curing by cross-linking performance.
[0062] Namely, a stock solution for production of nonlinear-optical
materials containing a cross-linkable nonlinear-optically active
organic compound having a hydrolyzed silyl group is produced, by
using a solid catalyst as the hydrolysis catalyst in a solution
containing a nonlinear-optically active organic compound having one
or more hydrolysable silyl groups as the cross-linkable functional
group, bringing the solution into contact with the solid catalyst,
and thus hydrolyzing the hydrolysable silyl group (hydrolysis
treatment); and then removing the solid catalyst from the solution
(catalyst-separation treatment).
[0063] In addition to the hydrolysis and separation treatments
above, any other optional treatments of the stock solution
according to the invention may be added before, during and/or after
the two steps. Details about the hydrolysis and separation
treatments will be described in detail below.
[0064] This stock solution is stable as it contains no catalyst and
exhibits a drastically longer pot life than conventional
homogeneous catalyst systems. As the hydrolysable silyl group is
already hydrolyzed to a polycondensable hydroxysilyl group, a
dehydration condensation reaction easily progresses when heated at
a temperature higher than the boiling temperature of water
(100.degree. C.), leading to curing by cross-linking. Accordingly,
the method above allows both an excellent pot life at room
temperature and high curing by cross-linking performance during
electric-field poling (performed commonly at a temperature of not
less than 100.degree. C.).
[0065] In the invention, use of a compound represented by the
Formula (1) as the nonlinear-optically active organic compound
according to the method above allows production of stock solutions
stable at higher concentration and of nonlinear-optical materials
having a desirable film thickness consistently without the problem
of aggregation or crystallization even when coated with this stock
solution. The nonlinear-optically active organic compound described
above has excellent nonlinear-optical characteristics, and thus
elements containing the compound exhibit more excellent
characteristics than ever in operating voltage, size and the like
and expand the possible application areas as will be described
below.
[0066] Stock solutions excellent both in pot life and curing by
cross-linking performance may be obtained, by adding a metal
chelate catalyst as the hydrolysis catalyst to a solution
containing the nonlinear-optically active organic compound having
one or more hydrolysable silyl groups as the cross-linkable
functional group and hydrolyzing the hydrolysable silyl group
(hydrolysis treatment); adding an anticatalyst that inhibits the
catalytic activity of the metal chelate catalyst to the solution
(termination treatment); and thus producing a stock solution for
production of nonlinear-optical materials containing a
cross-linkable nonlinear-optically active organic compound having a
hydrolyzed silyl group.
[0067] Metal chelate compounds described in a non-patent document
(Nippon Kagaku Kaishi, 1998, No. 9, pp. 571 to 579), and aluminum
alkoxides, titanium alkoxides, zirconium alkoxides, or the like
having at least one chelating agents including acetylacetone,
quinolinol, and the like may be used effectively as the metal
chelate catalysts.
[0068] Multidentate ligands having a greater chelating potential
are effective as the anticatalyst, and typical examples thereof
include acetylacetone, quinolinol, and the like.
[0069] During the hydrolysis using the solid catalyst or metal
chelate catalyst, polycondensation reaction may also progress in
parallel with the hydrolysis reaction. However, the
polycondensation reaction may be stopped practically anytime by
removing a solid catalyst when the solid catalyst is used or by
adding an anticatalyst when a metal chelate catalyst is used, which
ensures an elongated pot life of the solution.
[0070] The second stock solution according to the invention is a
stock solution for production of nonlinear-optical materials by wet
coating method, containing at least one nonlinear-optically active
organic compound represented by the following Formula (2) and a
matrix-forming compound having one or more cross-linkable
functional groups. 9
[0071] In the formula above, Z.sup.4 to Z.sup.6 each are
independently an aromatic group which may have substituents; D is a
.pi.-conjugated group which may have substituents; E is an
electron-withdrawing group which may have substituents; n is 0 or
1; and Z.sup.4 to Z.sup.6, D, and E each may be linked with any
other group to form a ring structure and may have one or more
cross-linkable functional groups.
[0072] From the viewpoints of chemical stability, nonlinear-optical
characteristics, and the like, E is preferably a .pi.-conjugated
electron-withdrawing group, which contains a ring structure and may
have substituents.
[0073] In addition, the Formula (2) preferably includes a
.pi.-conjugation system that spans both ends of the Z.sup.6-D.sub.n
structure formed from five or more consecutive unsaturated bonds.
The .pi.-conjugation system more preferably has 7 or more
conjugated bonds, and the upper limit of the number of conjugation
is about 15, from the viewpoint of ensuring the oxidation
resistance and aggregation resistance.
[0074] The second stock solution above contains, in addition to a
nonlinear-optically active organic compound having a cross-linkable
functional group, a matrix-forming compound having one or more
cross-linkable functional groups. In a similar manner to the
nonlinear-optically active organic compound having a cross-linkable
functional group for the first stock solution, this matrix-forming
compound also contributes to film forming by three-dimensional
cross-linking of the cross-linkable functional groups, but the
matrix-forming compound, which does not have a nonlinear-optically
active structure such as that in the nonlinear-optically active
organic compound, provides the resulting films cross-linked
together with the nonlinear-optically active organic compound with
favorable characteristics such as flexibility and the like due to
the structure of the matrix-forming compound.
[0075] The cross-linkable functional groups in the matrix-forming
compounds are not particularly limited, and include groups similar
to those described for the cross-linkable functional groups for the
first stock solution. Among them, substituted or unsubstituted
hydrolysable silyl groups are particularly preferable as they
provides cross-linked and cured films excellent in optical quality,
mechanical strength, solvent resistance, chemical stability, and
the like. On the other hand, the preferred structure, preferred
cross-linkable functional group, and the like of the
nonlinear-optically active organic compound are similar to those
described for the cross-linkable functional groups for the first
stock solution, except that the nonlinear-optically active organic
compound may not have a cross-linkable functional group.
[0076] Details about the matrix-forming compounds will be described
below.
[0077] Because the matrix-forming compound in the second stock
solution indispensably contains a cross-linkable functional group
as described above, the nonlinear-optically active organic compound
need not have a cross-linkable functional group. In such a case,
the nonlinear-optically active organic compound is present as
dispersed in the three-dimensionally cross-linked matrix-forming
compound.
[0078] If hydrolysable silyl groups are used as the cross-linkable
functional groups of the matrix-forming compound and the
nonlinear-optically active organic compound as in the case of the
first stock solution, all cross-linkable functional groups need not
be but are preferably the hydrolysable silyl groups.
[0079] In the second stock solution, matrix-forming compounds
having two or more hydrolysable silyl group are preferably used as
the matrix-forming compounds having one or more cross-linkable
functional groups, and nonlinear-optically active organic compounds
having one or more hydrolysable silyl groups are particularly
preferably used for increasing the cross-linking density of the
final cross-linked films.
[0080] The mixing ratio of the nonlinear-optically active organic
compound represented by the Formula (2) to the matrix-forming
compound (nonlinear-optically active organic
compound/matrix-forming compound) is preferably in the range of
1/99 to 95/5, and more preferably in the range of 20/80 to 80/20 by
weight.
[0081] In the similar manner to the first stock solution, with
respect to the second stock solution according to the invention,
the solution containing a nonlinear-optically active organic
compound and a matrix-forming compound is particularly preferably
subjected at least to the hydrolysis treatment wherein the
hydrolysable silyl group is hydrolyzed by bringing it into contact
with a solid catalyst and the catalyst-separation treatment wherein
the solid catalyst is removed from the solution after the
hydrolysis treatment; or, at least to the hydrolysis treatment
wherein the hydrolysable silyl group is hydrolyzed by adding a
metal chelate catalyst and the termination treatment wherein the
catalytic activity of the metal chelate catalyst in the stock
solution is inhibited by addition of an anticatalyst after the
hydrolysis treatment; for the purpose of improving the pot life,
curing by cross-linking performance, and the like of the stock
solution.
[0082] Hereinafter, the nonlinear-optically active organic compound
having one or more hydrolysable silyl groups, the hydrolysis and
catalyst separation steps using a solid catalyst, other components
contained in the stock solution, solvents used for the stock
solution, and the matrix-forming compound having hydrolysable silyl
groups used in the second stock solution, all common to the first
and second stock solutions according to the invention, will be
described in that order. Nonlinear-optically active organic
compound having one or more hydrolysable silyl groups.
[0083] The nonlinear-optically active organic compound having one
or more hydrolysable silyl groups favorably used in the invention
is a compound represented by the following Formula (3):
G(--Y).sub.j Formula (3)
[0084] In Formula (3), j is an integer of 1 or more; G is a group
wherein a binding bond for binding to Y is introduced to a site in
the nonlinear-optically active organic compound represented by the
Formula (1) or (2) [if a cross-linkable functional group is
contained in the nonlinear-optically active organic compound
represented by the Formula (2)].
[0085] The binding bond is not particularly limited if it can form
a bond between G and Y, and specific examples thereof include
hydrocarbon groups represented by --C.sub.nH.sub.2n--,
--C.sub.(n+1)H.sub.2n--, and --C.sub.(n+1)N.sub.(2n-2)-- (wherein,
n is an integer of 1 to 15); --CO--, --COO--, --NHCO--, --S--,
--O--, --N.dbd.CH--, --N.dbd.N--, a phenylene group, and the
derivatives thereof having substituents; and the combinations
thereof; and the like.
[0086] The binding bond may be introduced to any site of Z.sup.1 to
Z.sup.3, L, or A in Formula (1), or of Z.sup.4 to Z.sup.6, D, or E
in Formula (2), but the binding site and the structure of the
binding bond are properly selected so that at least the
nonlinear-optical characteristics are not damaged.
[0087] Y in the Formula (3) is represented by the following Formula
(4):
--SiR.sub.nQ.sub.(3-n) Formula (4)
[0088] In Formula (4), R represents a hydrogen atom, a substituted
or unsubstituted alkyl group, or a substituted or unsubstituted
aryl group. The alkyl group is not particularly limited, but
preferably a group having 1 to 20 carbons, and more preferably a
group having 1 to 15 carbons. The aryl group is preferably a group
having three or less aromatic rings.
[0089] Q represents a hydrolysable group, and n an integer of 0 to
2.
[0090] Therefore, Y is a hydrolysable silyl group, which is
converted to a hydroxysilyl group (silanol group) by hydrolysis of
the hydrolysable group Q and forms a cross-linked matrix by
dehydration condensation with other hydroxysilyl groups. Q is an
alkoxy, arylhydroxy, dialkylamino or alkylcarboxy group, a halogen
atom, or the like, but preferably an alkoxy group. If the number of
Y is increased, the cross-linking density, mechanical strength and
stability of the resulting nonlinear-optical materials are
improved, but on the contrary, the orientation by poling is
hindered. Accordingly, j is preferably an integer of 1 to 3.
[0091] The number of the hydrolysable group Q is 1 to 3, but if the
number of hydrolysable group Q is 3, the polycondensation reaction
may proceed in the stock solution rapidly, reducing the pot life
thereof, as the reactivity of the hydrolysable silyl group are
significantly high.
[0092] In such a case, reduction of the number of hydrolysable
group Q in the hydrolysable silyl group to 1 or 2 and introduction
of the structure R replacing the hydrolysable silyl group can
reduce the reactivity and extend the pot life of the stock
solution.
[0093] In addition, if the hydrolysable group Q is an alkoxy group,
the reactivity decreases in the order of bulkiness, i.e., methoxy
group >ethoxy group >propoxy group, and if, for example, a
methoxy group causes the problem in pot life, introduction of an
isopropoxy group replacing the methoxy group can elongate the pot
life of the stock solution.
[0094] Typical examples of the nonlinear-optically active organic
compounds having one or more hydrolysable silyl groups represented
by Formula (3) include the following compounds. In these
compound's, "Me" represents a methyl group, "Et" an ethyl group,
and "Pro" an isopropyl group.
[0095] When used together with a matrix-forming compound having one
or more cross-linkable functional groups, the nonlinear-optically
active organic compound represented by Formula (2) needs not have a
cross-linkable functional group, but preferably have one or more
cross-linkable functional groups, from the viewpoints of stability,
optical quality, and the like. 1011
[0096] Matrix Forming Compound Having One or More Hydrolysable
Silyl Groups
[0097] The matrix-forming compounds having hydrolysable silyl
groups favorably used in the second stock solution according to the
invention are represented by the following Formula (5):
T(--X).sub.i Formula (5)
[0098] In Formula (5), T is an aliphatic hydrocarbon group having 2
to 20 carbons which may have a branched chain, a ring structure, an
unsaturated bond, or a hetero atom; a substituted or unsubstituted
aromatic group; a hetero atom-containing aromatic group substituted
or unsubstituted; or a combination thereof, which may have
additionally at least one group selected from --NH--, --CO--,
--O--, --S--, and --Si--. X represents a hydrolysable silyl group
having a structure substantial identical with the structure
represented by Formula (4) in the similar manner to Y in the
Formula (3) (wherein, R, Q, and n in Formula (4) are independent
respectively in Y and X). Further, i is an integer of 1 or
more.
[0099] A plurality of nonlinear-optically active organic compounds
having one or more hydrolysable silyl groups represented by the
Formula (1) may be used together in the first stock solution
according to the invention, and a plurality of nonlinear-optically
active organic compounds having one or more hydrolysable silyl
groups represented by the Formula (2) and a plurality of
matrix-forming compounds having hydrolysable silyl groups may be
used together in the second stock solution. In such cases, the
hydrolysable silyl groups may have the same structure or different
structures respectively, but preferably have at least similar
hydrolysable groups Q, which are hydrolyzed in a similar manner,
because these compounds are cocross-linked more uniformly.
[0100] The structure represented by T in Formula (5) provides the
matrix-forming compound having hydrolysable silyl groups with a
suitable degree of flexibility, and thus exerts favorable effects
of absorbing the shrinkage deformation in the curing by
cross-linking step and thus preventing generation of cracks; and
reducing the concentration of hydroxysilyl groups remaining
uncross-linked when a cross-linked cured film is formed by using
the stock solution according to the invention containing the same.
Although the advantageous effects may be exerted by a
matrix-forming compound having only one hydrolysable silyl group,
but the effects are particularly significant when T is an organic
group having two or more carbons which may have substituents and
two or more hydrolysable silyl groups at the terminals of the
matrix-forming compound. Examples of these hydrolysable silyl
group-containing matrix-forming compounds are as follows: 1213
[0101] The upper limit of the number i of the hydrolysable silyl
groups in Formula (5) is not particularly limited, but preferably
not more than four. If i is larger than 4, the cross-linked matrix
formed is less flexible, sometimes leading to problems of
generation of cracks, a greater number of hydroxysilyl groups
remaining uncross-linked, and the like.
[0102] The matrix-forming compounds having hydrolysable silyl
groups are not limited to the examples above, and any publicly
known compounds used in the ordinary sol-gel process may also be
utilized. Examples thereof include tetramethoxysilane,
tetraethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane,
vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane,
3-glycidoxypropylmethyldiethoxysilane,
3-glycidoxypropyltrimethoxysilane,
3-glycidoxypropyltriethoxysilane, 3-aminopropyltriethoxysilane,
3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane,
N-(2-aminoethyl)-3-aminopropyltrietho- xysilane, and the like.
[0103] In addition, any component co-cross-linkable with a
hydroxysilyl group may be added as needed to the first and second
stock solutions. For example, alkoxide derivatives of metals such
as germanium, titanium, zirconium, and aluminum may be added for
the purpose of increasing the refractive index of the resulting
optical materials.
[0104] Hydrolysis and Catalyst-Separation Treatments
[0105] The stock solution according to the invention is preferably
prepared by subjecting a solution containing the compounds having
one or more hydrolysable silyl groups to the hydrolysis and
catalyst-separation treatments as will be described below.
[0106] A solid catalyst is preferably used as the catalyst for
promoting the hydrolysis of the hydrolysable silyl groups. As
described above, when a stock solution was prepared by sol-gel
process using the compound having one or more hydrolysable silyl
groups, easily soluble homogeneous catalysts including acid
catalysts such as hydrochloric acid and acetic acid, base catalysts
such as pyridine and triethyl amine, and the like have been
conventionally used as the catalyst.
[0107] These catalysts show catalytic activity not only in the
hydrolysis reaction but also in the subsequent polycondensation
reaction. Although the method employing the homogeneous catalyst is
convenient, the reactivity is too high and it is difficult to
remove the catalyst form the stock solution and stop the catalytic
reactions practically at a desired level, consequently leading to
the problems in controlling the quality and the pot life of the
stock solution and the like.
[0108] In contrast if a solid catalyst is used, the hydrolysis
reaction proceeds at a slower speed only on the surface of the
solid, and it becomes easier to control the progress of reaction
and avoid undesirable side reactions. Further as the catalyst can
be removed by a simple operation such as filtration, solid
catalysts have an advantage that the hydrolysis and subsequent
polycondensation reactions can be stopped at a desired level.
[0109] The solid catalyst is not particularly limited if it is
insoluble in the solution and the hydrolysable silyl group gives a
hydroxysilyl group by hydrolysis, and specific examples thereof are
described below. These catalysts may be used alone or in
combination.
[0110] Examples of the solid catalysts include ion exchange resins
such as AMBERLITE.RTM. 15, AMBERLITE.RTM. 200C, AMBERLYST.RTM. 15,
and AMBERLYST.RTM. 15E (heretofore, manufactured by Rohm and Haas
Company); DOWEX.RTM. MWC-1-H, DOWEX.RTM. 88, and DOWEX.RTM. HCR-W2
(heretofore, manufactured by Dow Chemical); Lewatit.RTM. SPC-108
and Lewatit.RTM. SPC-118 (heretofore, manufactured by Bayer);
DIAION RCP-150H (trade name, manufactured by Mitsubishi Chemical
Corporation); Sumikaion KC-470, Duolite C26-C, Duolite C-433, and
Duolite-464 (heretofore, manufactured by Sumitomo Chemical);
Nafion.RTM.-H (manufactured by Du Pond); and Purolite (manufactured
by AMP Ionex);
[0111] solid acids having a compound containing a protonic acid
group such as Zr(O.sub.3PCH.sub.2CH.sub.2SO.sub.3H).sub.2 and
Th(O.sub.3PCH.sub.2CH.sub.2COOH).sub.2 bound to the surface
thereof; polyorganosiloxanes containing a protonic acid group such
as polyorganosiloxanes containing a sulfonic acid group; heteropoly
acids such as cobaltic/tungstic acid and phosphomolybdic acid;
isopoly acids such as niobic acid, tantalic acid, and molybdenic
acid; single metal oxides such as silica gel, alumina, chromia,
zirconia, CaO, and MgO; complex metal oxides such as
silica-alumina, silica-magnesia, silica-zirconia, and zeolites;
[0112] clay minerals such as acid clay, activated clay,
montmorillonite, and kaolinite; metal phosphate salts such as
zirconia phosphate and lanthanum phosphate; solid bases having a
compound containing an amino group bound on the surface thereof
such as solids obtained by reacting 3-aminopropyltriethoxysilane
with the surface of silica gel; polyorganosiloxanes having an amino
group such as amino-modified silicone resins; and the like.
[0113] For preparation of stock solutions using the solid catalyst
above, it is necessary at least to subject the solution to a
hydrolysis step wherein it is brought into contact with the solid
catalyst and hydrolyzed and to a catalyst-separation step wherein
the solution after the hydrolysis step is separated from the solid
catalyst.
[0114] The hydrolysis step is not particularly limited, if the step
allows hydrolysis by bringing the solution into contact with the
solid catalyst for a certain time. The kind, amount, shape, and the
like of the solid catalyst used are selected properly according to
the processing conditions (temperature and the like) and the
matrix-forming compound and/or nonlinear-optically active organic
compound present in the stock solution, so that desired coatability
and film thickness can be obtained. The catalyst-separation step is
also not particularly limited, if the step can eliminate the solid
catalyst in the solution after the hydrolysis step.
[0115] The contact to and removal from the solid catalyst of the
solution in the hydrolysis and catalyst-separation steps may be
continuously performed by passing the solution through a column
filled with porous or fibrous carriers supporting the solid
catalyst. Alternatively, such processing may be performed
batchwise. For example, after hydrolysis by dispersing a
particulate solid catalyst in the solution, the solid catalyst may
be filtered through a filter such as filter paper, filter cloth,
membrane filter, glass filter, cotton filter, or the like under
atmospheric, reduced, or increased pressure; or after the solution
is stirred for a certain time in a reaction container having the
solid catalyst coated on the internal wall thereof, the solution
may be transferred to another container.
[0116] The amount of the solid catalyst used is not particularly
limited, but preferably in the range of 0.001 to 20%, more
preferably in the range of 0.01 to 10% by mass with respect to the
total amount of the compounds having one or more hydrolysable silyl
groups contained in the stock solution.
[0117] The temperature of the reaction with the solid catalyst may
vary depending on the kinds of the solid catalyst used and the
components contained in the stock solution, but usually in the
range of 0 to 100.degree. C., more preferably in the range of 5 to
70.degree. C., and particularly more preferably in the range of 10
to 50.degree. C.
[0118] The reaction time varies depending on the method of contact
between the solid catalyst and the stock solution and also on the
temperature of reaction, but is preferably in the range of 10
minutes to 100 hours, as a prolonged reaction time may lead to
gelation of the solution.
[0119] Other Additives
[0120] The solution obtained after hydrolysis and
catalyst-separation may be used as it is as the stock solution, but
the following various additives may be added as needed.
[0121] To the stock solution according to the invention, it is
preferable to add a curing catalyst for accelerating the curing by
cross-linking reaction, in particular, a curing catalyst that is
activated by energy such as heat or light provided externally, from
the viewpoint of pot life.
[0122] The curing catalyst should be selected properly according to
the cross-linkable functional groups used, and examples thereof
include protonic acids such as hydrochloric acid, acetic acid,
phosphoric acid, and sulfuric acid; bases such as ammonia and
triethyl amine; organic tin compounds such as dibutyltin diacetate,
dibutyltin dioctanoate; titanium compounds such as titanium
tetrabutoxide, titanium tetraisopropoxide, and
acetylacetonatotitanium tributoxide; zirconium compounds such as
acetylacetonatozirconium tributoxide; aluminum compounds such as
aluminum tributoxide, triacetylacetonatoaluminium, and aluminum
triacetylacetate; iron, manganese, cobalt, zinc, and zirconium
salts of organic carboxylic acids; publicly known photochemical
radical generators: publicly known thermal radical generators;
publicly known photochemical acid generators; publicly known
photochemical base generators; and the like.
[0123] In particular when the cross-linkable functional group
according to the invention is a hydrolysable silyl group,
acetylacetonato complexes of metals are preferable among them from
the viewpoints of the storage stability of stock solution, the
adverse effects of residual catalyst, and the like. In such a case,
addition of acetylacetone may further increase the storage
stability of the stock solution.
[0124] If one of the homogeneous catalysts described above
including protonic acids, such as hydrochloric acid, acetic acid,
phosphoric acid, and sulfuric acid, is used as the curing catalyst,
addition thereof should be reduced to the minimum amount required
for practically promoting the catalytic reaction by heating, for
prevention of the decrease in pot life at room temperature.
[0125] The amount of the curing catalyst added is not particularly
limited, but preferably in the range of 0.1 to 20%, more preferably
in the range of 0.3 to 10% by mass with respect to the total amount
of the compounds having one or more cross-linkable functional
groups contained in the stock solution, from the viewpoints of the
pot life, curing temperature, and others of the stock solution.
[0126] To the stock solution according to the invention, for
example, a publicly known antioxidant such as
2,6-di-t-butyl-4-methylphenol and hydroquinone may be added for
prevention of oxidative degradation of the nonlinear-optically
active organic compound; and a publicly known UV absorbent such as
2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzop- henone may
be added for prevention of ultraviolet degradation of the
nonlinear-optically active organic compound. Further, a publicly
known leveling agent such as a silicone oil may be added for the
purpose of improving smoothness of the surface of coated films; a
publicly known polycondensation inhibitor, for improving the pot
life; a publicly known curing aid, for accelerating curing by
cross-linking; or a publicly known functional material for granting
a function other than the nonlinear-optical function.
[0127] In addition, a resin such as polyvinyl alcohol, polyvinyl
butyral, polyvinyl acetal, polyurethane, polyamide, polyvinyl
acetate, polyvinylpyrrolidone, polyvinylpyridine, or a polymeric
compound having an alkoxy silyl group as the side chain, or a
copolymer thereof may be added for the purpose of adjusting
(thickening) the viscosity of the stock solution.
[0128] The solvents used for the stock solution include alcohols
(e.g., methanol, ethanol, propanol, butanol, and the like), ketones
(e.g., acetone, methylethylketone, cyclopentanone, cyclohexanone,
and the like), ethers (e.g., tetrahydrofuran,
2-methyltetrahydrofuran, diethylether, dioxane, and the like),
esters (e.g., ethyl acetate and isopropyl acetate), aromatic
compounds (e.g., benzene, toluene, xylene, chlorobenzene and
tetrahydronaphthalene), amides (e.g., dimethylformamide and
dimethylacetamide), dimethylsulfoxide, and the like. These solvents
may be used alone or in combination of two or more solvents.
[0129] The content of the solvent in stock solution is not
particularly limited, but as solid matters tend to precipitate if
the solvent content is too low, the content of the components other
than solvent in the stock solution is preferably adjusted in the
range of 0.5 to 30% by mass.
[0130] When a compound having one or more hydrolysable silyl groups
is used as the cross-linkable functional group, water should be
added to the stock solution at least in the hydrolysis step. The
amount of added water is not particularly limited, but is
preferably in the range of 30 to 500% by mole, more preferably in
the range of 50 to 300% by mole with respect to the theoretical
amount required for complete hydrolysis of all hydrolysable silyl
groups contained in the solution, for improving the storage
stability of stock solution and suppressing sedimentation and phase
separation of the organic components in the stock solution.
[0131] A water content of more than 500% by mole may lead to
deterioration of the storage stability of stock solution and
precipitation of organic components. The problem may be avoided
sometimes by mixing with an alcohol. On the other hand, a water
content of less than 30% by mole may leave most of the hydrolysable
silyl groups unhydrolyzed, making the curing by cross-linking more
difficult to proceed.
[0132] The added water still remaining after the hydrolysis
reaction may be removed by distillation, absorption, or the
like.
[0133] Nonlinear-Optical Material
[0134] Hereinafter, nonlinear-optical materials prepared by using
the stock solution according to the invention will be
described.
[0135] The production method and the shape of the nonlinear-optical
materials according to the invention are not particularly limited
if the materials are produced using the stock solution according to
the invention. For example, bulk nonlinear-optical materials may be
produced by pouring the stock solution into a mold and curing by
cross-linking the solution therein, or film-shaped
nonlinear-optical materials, by coating the stock solution onto the
surface of substrates in any shape including plate and fiber and
curing by cross-linking the solution thereon.
[0136] Hereinafter, nonlinear-optical materials and processes of
manufacturing the same will be described, assuming that a thin-film
nonlinear-optical material is produced by coating a stock solution
on a substrate surface.
[0137] The method of coating the stock solution is not particularly
limited, and examples thereof include publicly known wet coating
methods such as spin-coating, spray-coating, blade-coating,
dip-coating, and ink jet methods.
[0138] After coated on the substrate surface, the stock solution is
cross-linked and cured. The curing by cross-linking may be caused
naturally by evaporation of the solvent under ambient environment,
but it is more preferable to remove the solvent forcibly, for
example, under reduced pressure and then cause the curing reaction
by the heat, ultraviolet irradiation, or the like supplied
externally by using the curing catalyst previously added to the
stock solution.
[0139] To induce a second-order nonlinear-optical activity in a
nonlinear-optical material, it is necessary, as described above, to
orient the nonlinear-optically active organic compound by some
orientation means.
[0140] One of the methods for orienting the nonlinear-optically
active organic compound is to apply a stock solution onto a
substrate having an oriented film on the surface thereof and induce
orientation of the nonlinear-optically active organic compound
contained in the nonlinear-optical material by the orientation of
the oriented film. Alternatively, publicly known poling methods
such as photopoling, photoassisted electric-field poling, and
electric-field poling may also be effectively used. Among them, the
electric field-poling method is particularly preferable, from the
points of the convenience of equipment, the degree of orientation
of the resulting films, and the like.
[0141] The electric field-poling method is an orientation method of
orienting a nonlinear-optically active organic compound in the
direction of applied electric field, by mutual interaction of the
dipole moment of the nonlinear-optically active organic compound
and the Coulomb force of the applied electric field. In the process
by the electric field-poling method, the orientation of the
nonlinear-optically active organic compound in the direction of
electric field is commonly accelerated by heating while the
electric field is applied and terminating the application of
electric field after sufficient orientation is induced. The
electric-field poling of the cross-linkable nonlinear-optical
material according to the invention is performed during or before
curing by cross-linking. In this manner, the orientation induced by
the electric-field poling is frozen or stabilized by curing by
cross-linking.
[0142] Accordingly, the orientation treatment in an elastic state
and subsequent cross-link and curing treatment enable stabilization
of the oriented state, allowing a high degree of orientation and
the preservation of the induced orientation. However, if the
orientation treatment by electric-field poling is attempted in a
state completely without curing by cross-linking at all, the
resistance of the film is so low that an effective poling electric
field cannot be applied, sometimes resulting in a low degree of
orientation. The problem may be avoided by partially progressing
the curing by cross-linking reaction before the electric-field
poling treatment or by employing a photoassisted electric
field-poling or photopoling method as the orientation method.
[0143] When the heat-curing and electric-field poling treatments
are performed at the same time, the temperature may be raised
rapidly to the curing-reaction temperature while applying an
electric field, but in such a case, the curing reaction progresses
rapidly before sufficient orientation is induced, restricting the
movement of the nonlinear-optically active organic compound and
consequently prohibiting effective orientation.
[0144] Therefore, methods of raising the temperature gradually or
stepwise while applying an electric field are more effective in the
case above.
[0145] The intensity of the applied electric field during the
electric-field poling treatment may be constant or varied
continuously or stepwise. Alternatively, an electric field changing
periodically may also be applied.
[0146] Any one of the methods known in the art may be used as the
method for applying electric field to the nonlinear-optical
material in the electric-field poling treatment, and examples
thereof include discharge methods of discharging a
nonlinear-optical material by using a needle-shaped, wire-shaped,
comb-shaped, plate-shaped, or other electrode, or an electrode
above having an additional grid electrode connected thereto; and
contact-electrode methods of applying an electric field by
connecting a pair of electrodes to the nonlinear-optical
material.
[0147] In the case of the contact-electrode methods above, the
electrodes may be formed directly on the surface of
nonlinear-optical material, or the electrodes may be brought to the
vicinity of or into contact with the nonlinear-optical material
only during the electric-field poling treatment. Materials for the
electrodes which may be formed on the film surface include various
metals such as gold, aluminum, nickel, chromium, and palladium, and
the alloys thereof; electrically conductive metal oxides;
electrically conductive polymers; and the like.
[0148] Commonly practiced vapor deposition and spattering may be
used as the method for forming electrodes directly on the film
surface. The electrode materials above and those having a
conductive film formed on a nonconductive substrate surface such as
glass and plastics may be used as the electrodes which are brought
to the vicinity of or into contact with the film.
[0149] The electric-field poling treatment may be performed in the
air, but is preferably performed under an inactive gas such as
nitrogen or argon or under reduced pressure. The discharge method
under such an environment provides advantages of allowing
prevention of degradation of the nonlinear-optical material due to
oxygen in the air, discharge products, or the like, and of
unnecessary spark discharge often found when a high-electric field
is applied by the electrode method.
[0150] Nonlinear-Optical Device
[0151] The nonlinear-optical material according to the invention
thus obtained may be applied to any devices in any shape that use
the nonlinear-optical function, for example, to
wavelength-converting devices in the shape of a thin film formed on
a transparent substrate. It may also be applied to the core or
other layers for electro-optical devices having a waveguide
structure.
[0152] Hereinafter, a waveguide-type electro-optical device having
a core layer formed with the nonlinear-optical material according
to the invention, a preferable embodiment of the present invention
will be described in detail.
[0153] The favorable configurations of the waveguide-type
electro-optical device, a nonlinear-optical device according to the
invention, are not particular limited, and include various
configurations. For example in devices consisting of a plurality of
layers, at least one layer thereof may be formed with the stock
solution according to the invention, but the core layer wherein the
light transmits is preferably formed with the stock solution
according to the invention. In such a case, the materials used for
other layers are not particularly restricted.
[0154] Examples of the configuration of waveguide-type
electro-optical devices, nonlinear-optical devices according to the
invention, are shown as schematic cross-sectional views in FIGS. 1
to 4.
[0155] The waveguide-type electro-optical device preferably has a
configuration comprising at least a lower cladding layer and a core
layer on the substrate surface, and preferably a configuration as
shown in FIG. 1 wherein an upper cladding layer 2 is also
constructed.
[0156] When used as the core layer for waveguide-type
electro-optical devices, the nonlinear-optical material according
to the invention provides the resulting device with excellent
nonlinear-optical characteristics and ensures high stability. When
used as the core layer for nonlinear-optical materials according to
the invention, the nonlinear-optical material according to the
invention prevents the problem of erosion of the core layer, when
an upper cladding layer is additionally formed on the
aforementioned polymeric nonlinear-optical material or when
patterning of the core layer and the top electrode is performed, as
will be described below.
[0157] In the waveguide-type electro-optical devices prepared from
the nonlinear-optical device according to the invention, a pair of
electrodes for applying an electric field should be connected to at
least to the layer containing the nonlinear-optical material
according to the invention for driving the devices. As shown in
FIG. 1, a pair of electrodes, bottom electrode 5 and top electrode
1, preferably sandwiches the waveguide layer consisting of a lower
cladding layer 4, a core layer 3, and an upper cladding layer
2.
[0158] The materials constituting the substrate 6 include metals
such as aluminum, gold, iron, nickel, chromium, and titanium;
semiconductors such as silicon, gallium-arsenic, indium-phosphorus,
titanium oxide, and zinc oxide; ceramics such as glass; plastics
such as polyethylene terephthalate, polyethylene naphthalate,
polycarbonate, polysulfone, polyether ketone, and polyimide; and
the like.
[0159] An electrically conductive film may be formed on the surface
of these substrate materials, and the materials for the
electrically conductive films include metals such as aluminum,
gold, nickel, chromium, and titanium; electrically conductive
oxides such as tin oxide, indium oxide, ITO (mixed tin and indium
oxide); electrically conductive polymers such as polythiophene,
polyaniline, poly-p-phenylene vinylene, and polyacetylene; and the
like. These electrically conductive films may be formed by any one
of the publicly known dry coating methods such as vapor deposition
and spattering; or of publicly known wet coating methods such as
spray coating, dip-coating, and electrolytic precipitation, and
patterns may be formed thereon as needed. The electrically
conductive substrates or the electrically conductive films formed
on substrates are used as electrodes (e.g., bottom electrode 5 in
FIG. 1) for electric-field poling and for driving devices.
[0160] In addition, an adhesion layer for improving the adhesion
between the substrate 6 and the film formed thereon, a leveling
layer for smoothing the depression and projection of substrate
surface, or an intermediate layer for providing these functions
concurrently may be formed on the surface of substrate 6 as
needed.
[0161] The materials used for forming these layers are not
particularly limited, and examples thereof include publicly known
materials including acrylic resin, methacrylic resin, amide resin,
polyvinyl chloride resin, vinyl acetate resin, phenol resin,
urethane resin, vinyl alcohol resin, acetal resin, and the like, or
the copolymers thereof; and cross-linked or cocross-linked polymers
of zirconium alkoxide compounds, titanium alkoxide compounds, and
silane coupling agents; and the like.
[0162] As described above, nonlinear-optical device according to
the invention preferably has a waveguide structure having one or
more core layers and two cladding layers sandwiching the core
layers, and the nonlinear-optical material according to the
invention is particularly preferably contained in the waveguide
core layers.
[0163] A lower cladding layer 4 is preferably formed between the
substrate 6 and the core layer 3 containing the nonlinear-optical
material according to the invention. The lower cladding layer 4 may
be formed with any material, if it has a refractive index lower
than that of the core layer 3 and is not damaged when the core
layer is formed. Favorable materials there of include UV-curing or
thermosetting acrylic, epoxy, silicone, and other resins;
polyimide; SiO.sub.2; and the like. Alternatively, the
nonlinear-optical material according to the invention may also be
used. However in such a case, the structure, content, and others of
the nonlinear-optically active organic compound therein should be
adjusted so that it has a refractive index smaller than the
nonlinear-optically active organic compound used in the core layer
3.
[0164] After the core layer containing the nonlinear-optical
material according to the invention is formed, an upper cladding
layer 7 may additionally formed atop the core layer in the similar
manner to the lower cladding layer 4. Thus, a slab waveguide having
a configuration of cladding layer/core layer/upper cladding layer
shown in FIG. 1 is formed.
[0165] After the core layer 3 is formed, the core layer 3 may be
patterned to form a channel waveguide (FIG. 2) or a ridge waveguide
(FIG. 3), by any one of methods known in the art using a
semiconductor-processing technology such as reactive ion etching
(RIE), wet etching photolithography, electron-beam lithography, and
the like. Alternatively, the channel or ridge waveguide may be
formed by irradiating a part of the core layer 3 with patterned UV
light, electron beam, or the like, and thus changing the refractive
index of the irradiated portion. Further, a reverse-ridge waveguide
may also be formed by patterning the lower cladding layer 4 in
advance by any one of methods known in the art using a
semiconductor processing technology such as reactive ion etching
(RIE), wet etching, photolithography, electron-beam lithography and
the like, and forming a core layer 3 thereon.
[0166] A basic electro-optical device may be prepared by forming a
top electrode 1 for driving the device at a desired portion of the
surface of upper cladding layer 2.
[0167] Any one of coating methods publicly known such as
spin-coating, spray-coating, blade-coating, dip-coating, and ink
jet may be used as the method for forming the cladding layer above
and the core layer 3. The solvent therein may be removed by natural
evaporation or forcibly, for example, by heating in a heat dryer or
the like or under reduced pressure in a vacuum dryer or the
like.
[0168] If the cladding layer and the core layer 3 are formed with a
curing by cross-linking material such as the nonlinear-optical
material according to the invention, each layer may be cross-linked
and cured completely by heating or UV irradiation when the layer is
formed, or only partly to such a degree that the layer is not
eroded when another layer is coated thereon. In particular, if
there are problems of repellence when a layer is formed on another
layer and of improper adhesion of the two layers, partial curing by
cross-linking may sometimes remedy these problems. By keeping the
degree of curing by cross-linking of the lower cladding layer 4
only partial and the resistance thereof lower, it is possible to
apply a more effective poling electric field to the core layer 3
when the core layer 3 is subjected to an electric-field poling
treatment and thus to obtain a higher degree of orientation.
[0169] The film thickness of the lower cladding layer 4 may vary
according to the wavelength, mode, and the like of the light used,
but preferably in the range of about 0.1 to 2,000 .mu.m, and more
preferably in the range of about 1 to 100 .mu.m.
[0170] The film thickness of the core layer 3 varies according to
the wavelength, mode, or the like of the light used, but is
preferably in the range of about 0.1 to 500 .mu.m, and more
preferably in the range of about 0.5 to 50 .mu.m.
[0171] If the core layer 3 is formed with the nonlinear-optical
material according to the invention, it is preferable to conduct
heat curing and poling simultaneously after application of the
stock solution and removal of the solvent. The solvent removal and
the curing may be conducted at the same time. The methods similar
to those described for the nonlinear-optical material according to
the invention may be applied as the method for the poling
treatment.
[0172] In the case of electric-field poling treatment, the heating
temperature is preferably a temperature allowing almost complete
curing by cross-linking of the core layer 3 in the final phase, and
more specifically, it is preferable to keep the core layer at a
temperature in the range of 100 to 200.degree. C. for about 0.1 to
10 hours. If the poling temperature is raised stepwise from room
temperature to the final temperature, the difference between the
steps is preferably in the range of about 5 to 50.degree. C. and
the period of each step about 5 to 120 minutes, and the temperature
differences and the periods above may be the same or different. If
the poling temperature is raised continuously, the rate of
temperature increase is preferably about 0.1 to 20.degree. C./min.
The temperature may be raised both in the continuous and stepwise
manner.
[0173] The location of the electrode, grid, and sample surface is
arbitrary if they are in that order during treatment by the
discharge method, but the distance between the electrode and the
sample surface is preferably in the range of about 5 to 100 mm, and
the minimum distance between the grid and the sample surface is in
the range of about 1 to 30 mm. Use of the grid may sometimes
stabilizes discharging and allows prevention of the influx of
excessive ion stream onto the sample surface, thus providing an
advantageous effect of suppressing the damage of the sample surface
due to discharge products.
[0174] During the electric-field poling treatment, the voltage
applied to the electrode and the grid may be constant or changed
continuously or in stepwise, according to or not according to the
timing of temperature increase or decrease. For example, the
voltage applied to the electrode is preferably in the range of
about 1 to 20 kV, and the voltage applied to the grid when used, in
the range of about 0.1 to 2 kV.
[0175] Alternatively, the voltage applied to the electrode during
poling by the electrode method is preferably in the range of about
0.1 to 2 kV. The polarity of the electrode may be positive or
negative, but in the case of the discharge method, a positive
sample surface, i.e., positive discharge, enables reduction in the
amount of ozone, nitrous oxide, and the like generated by
discharging and thus in the degree of damage of the sample.
[0176] The total period of poling including the step for lowering
the temperature is preferably not more than 24 hours.
[0177] An indicator employed for examining whether the poling is
effective or not is a numerical value (order parameter: .phi.)
indicating how many nonlinear-optical molecules (generally
exhibiting dichroism) are oriented in the direction of electric
field. Specifically, if the absorbance when the molecules are
randomly oriented is designated as A0 and the absorbance when the
molecules are oriented in the electric-field direction
(film-thickness direction) as At, the value .phi. may be calculated
by the formula 1--(At/A0).
[0178] The order parameter above has a numerical value of 1 in the
ideal condition when all molecules are oriented completely, and 0
when the molecules are completely random, and thus a greater value
indicates a higher degree of orientation of molecules as a whole.
Determination of this value allows judgment of the efficiency of
poling and the stability of orientation.
[0179] In addition to materials similar to those for the lower
cladding layer described above, various thermoplastic resins
commonly used for polymer waveguides may be used for the upper
cladding layer 2. Examples of these thermoplastic resins include
polycarbonate, polyester, polyacrylate, polymethyl (meth)acrylate,
polyimide, polyamide, polystyrene, polycyclic olefin, and the like.
The core layer 3 according to the invention, which is already
cross-linked and cured, is superior in orientation stability and
solvent resistance and thus has an advantage that it provide a
greater number of options in selecting the coating method and the
material for the upper cladding layer and the solvent for coating
the same.
[0180] If an upper cladding layer 2 is formed on the surface of a
core layer 3, the poling treatment may be performed after the upper
cladding layer 2 is formed. For example, after the core layer 3 is
coated, and deprived of the solvent and partially cross-linked and
cured as needed, the poling treatment may be performed in the state
wherein an upper cladding layer 2 formed or in the state wherein a
top electrode 1 is additionally formed.
[0181] The film thickness of the upper cladding layer 2 varies
depending on the wavelength, mode, and the like of the light used,
but is preferably in the range of about 0.1 to 2,000 .mu.m, and
more preferably in the range of about 1 to 100 .mu.m.
[0182] If the nonlinear-optical device according to the invention
is used in the configuration of waveguide as described above, it is
necessary to make the refractive index of the cladding layer
smaller than that of the core layer 3 in order to confine the light
in the core layer 3 by the difference in refractive index. The
difference in refractive index between the core layer 3 and the
cladding layer varies according to the mode and the like. For
example, when used as a single-mode waveguide, the difference in
refractive index between the core layer 3 and cladding layer is
preferably in the range of 0.01 to 30%, and more preferably in the
range of 0.1 to 10%.
[0183] The method of patterning the core layer 3 by irradiating
patterned UV light described above is generally known by the name
of photobleaching method. In this case, publicly known lamps
including (high-pressure) mercury arc lamp, xenon short-arc lamp,
(metal) halogen lamp, black light, D2 lamp, various lasers, and the
like may be used as the UV light source. For example, if a
high-pressure mercury arc lamp is used, the irradiation intensity
is preferably about 5 to 1,000 mW, and the period of irradiation is
about 1 minute to 200 hours. If a mask pattern is used for
patternization, a method known in the art such as metal mask method
may be used as it is.
[0184] The step of patterning the core layer 3 by the
photobleaching method may precede the poling treatment if the core
layer is already coated, but preferably follows the cross-link
curing and poling treatment. Alternatively, the patterning may be
performed after the upper cladding layer 2 and the top electrode 1
are further formed.
[0185] When a channel or ridge waveguide is formed in the manner
described above, the pattern of the core layer 3 may be any one of
publicly known device structures such as straight line, Y-branched,
directional coupler, and Mach-Zehnder types, and in such a
configuration, the nonlinear-optical device according to the
invention can be applied to known optical telecommunication devices
such as optical switch, optical modulator, and phase-shifting
device.
EXAMPLES
[0186] Hereinafter, the present invention will be described in more
detail with reference to Examples, but it should be understood that
the invention is not limited thereto.
Example 1
[0187] Preparation of Stock Solution A
[0188] To a solution wherein the composition below is mixed and
dissolved well, 0.6 part by mass of an ion exchange resin
(AMBERLYST.RTM. 15E, manufactured by Rohm and Haas Company) is
added as a solid catalyst. The slurry is stirred and reacted
(hydrolysis treatment) at room temperature for one hour and
filtered through a membrane filter to remove the ion exchange resin
(catalyst-separation treatment). To the solution, 0.06 part by mass
of aluminum trisacetylacetonate and 0.06 part by mass of
acetylacetone are added respectively as a heat-curing catalyst and
a curing inhibitor, to give a stock solution A for production of
nonlinear-optical materials.
[0189] Nonlinear-optically active organic compound having two
hydrolysable silyl groups represented by Structural Formula (1-1):
1 part by mass
[0190] Distilled water: 0.2 part by mass
[0191] Methanol: 1 part by mass
[0192] Tetrahydrofuran: 4 parts by mass
[0193] Cyclohexanone: 18 parts by mass 14
[0194] The stock solution A is immediately transferred into a
sealed container and stored at room temperature and atmospheric
pressure, until the solution A is used for coating. The pot life of
the solution A under the sealed condition is determined by visual
observation. The solution is very stable as there are no change in
viscosity and no precipitation of solid matters observed after 10
days.
[0195] Preparation and Evaluation of Nonlinear-Optical Material
(Cross-Linked Cured Film A)
[0196] Subsequently, the stock solution A is coated onto an ITO
surface coated on a glass substrate (thickness: 1 mm; surface
resistance: 10 .OMEGA./.quadrature.) by the spin-coating method,
air-dried for 10 minutes, and additionally dried under reduced
pressure in a vacuum desiccator at room temperature for 12 hours,
to give sample A.
[0197] Subsequently, the coated sample A is placed on a hot plate
with the coated film facing upward and subjected to heat curing and
electric-field poling treatments, to give a nonlinear-optical
material according to the invention. The electric-field poling
treatment is performed by the discharge method using a scorotron
electrode, wherein the voltage applied to the wire electrode is 5
kV; the voltage applied to the grid electrode is 100 V; and the
distance between the coated film and the surface of grid electrode
is 2 mm. After application of the voltage, the temperature of the
hot plate is gradually raised from room temperature to 130.degree.
C. over a period of one hour, kept at 130.degree. C. for 30
minutes, and then lowered to room temperature over a period of
about 30 minutes under the conditions above, and then the
application of voltage is discontinued. In this manner, the
electric-field poling and heat curing are performed simultaneously,
to give a cross-linked cured film A (concentration of the
nonlinear-optically active compound backbone: about 60% by
mass).
[0198] The cross-linked cured film A after the electric-field
poling treatment is a glossy clear film without any defects
detectable by visual observation. The thickness of the film is
about 0.5 .mu.m.
[0199] In addition, evaluation of the change in poling state of the
crosslinked cured film A over time reveals that the order
parameters immediately after preparation and after stored in dark
place for 10 days are both 0.3 and there is no relaxation of the
orientation at all.
[0200] The order parameter is determined by measuring absorption
spectra of a cured film 1 prepared without the poling treatment
wherein the nonlinear-optically active compound is randomly
oriented, and a cured film 2 prepared with the poling treatment
wherein the nonlinear-optically active compound is oriented in the
film thickness direction, by using a spectrophotometer (U-3000,
manufactured by Hitachi); and calculating according to the
following Equation (1) form the absorptions thereof at the
wavelength of .lambda.max, at which the light absorption of the
cured films 1 and 2 is maximum.
.phi.=1-At/A0 Equation (1)
[0201] In Equation (1), .phi. represents an order parameter; At
represents the absorbance at the wavelength .lambda.max of the
cured film 2 after the poling treatment; and A0 represents the
absorbance at the wavelength .lambda.max of the cured film 1 before
poling treatment.).
[0202] Observation of second harmonics at 775 nm generated by
irradiation of a semiconductor laser beam having an oscillation
wavelength of 1550 nm onto the cross-linked cured film A thus
obtained confirms that the cross-linked cured film A, a
nonlinear-optical material according to the invention, has a
nonlinear-optical function. When the cross-linked cured film A is
further irradiated with a laser beam once again after stored at a
high temperature of 150.degree. C. for one hour, generation of
second harmonics at an intensity equivalent to that of the original
film is observed, which confirms that the nonlinear-optical
material according to the invention has high heat resistance.
[0203] The evaluation results above are summarized in Table 1.
Example 2
[0204] Preparation of Stock Solution B
[0205] To a solution wherein the composition below is mixed and
dissolved well, 0.6 part by mass of an ion exchange resin
(AMBERLYST.RTM. 15E, manufactured by Rohm and Haas Company) is
added as a solid catalyst. The slurry is stirred and reacted at
room temperature for one hour (hydrolysis treatment), and filtered
through a membrane filter to remove the ion exchange resin
(catalyst-separation treatment). To the solution, 0.06 part by mass
of aluminum trisacetylacetonate and 0.06 part by mass of
acetylacetone are added respectively as a heat-curing catalyst and
a curing inhibitor, to give stock solution B.
[0206] Nonlinear-optically active organic compound not having a
hydrolysable silyl groups represented by Structural Formula (2-1):
0.5 part by mass
[0207] Matrix-forming compound having two hydrolysable silyl groups
represented by Structural Formula (2-2): 1 part by mass
[0208] Distilled water: 2.5 parts by mass
[0209] Methanol: 6 parts by mass
[0210] N,N-dimethylformamide: 18 parts by mass 15
[0211] The stock solution B is immediately transferred into a
sealed container and stored at room temperature and atmospheric
pressure, until the solution A is used for coating. The pot life of
the solution A under the sealed condition is determined by visual
observation. The solution is very stable as there are no change in
viscosity and no precipitation of solid matters after 10 days.
[0212] Preparation and Evaluation of Nonlinear-Optical Material
(Cross-Linked Cured Film B),
[0213] Subsequently, cross-linked cured film B (concentration of
the nonlinear-optically active compound backbone: about 55% by
mass), a nonlinear-optical material according to the invention, is
prepared using the stock solution B in the similar manner to
Example 1, and the film characteristics, nonlinear-optical
characteristics, and the like are evaluated in the similar manner
to Example 1.
[0214] The evaluation results thus obtained are summarized in Table
1.
Example 3
[0215] Preparation of Stock Solution C
[0216] To a solution wherein the composition below is mixed and
dissolved well, 0.6 part by mass of an ion exchange resin
(AMBERLYST.RTM. 15E, manufactured by Rohm and Haas Company) is
added as a solid catalyst. The slurry is stirred and reacted at
room temperature for one hour (hydrolysis treatment), and filtered
through a membrane filter to remove the ion exchange resin
(catalyst-separation treatment). To the solution, 0.06 part by mass
of aluminum trisacetylacetonate and 0.06 part by mass of
acetylacetone are added respectively as a heat-curing catalyst and
a curing inhibitor, to give a stock solution C for production of
nonlinear-optical materials.
[0217] Nonlinear-optically active organic compound having a
hydrolysable silyl group represented by Structural Formula (3-1):
1.5 parts by mass
[0218] Matrix forming compound having two hydrolysable silyl groups
represented by Structural Formula (3-2): 0.5 part by mass
[0219] Distilled water: 1.5 parts by mass
[0220] Methanol: 6 parts by mass
[0221] Tetrahydrofuran: 18 parts by mass 16
[0222] The stock solution A is immediately transferred into a
sealed container and stored at room temperature and atmospheric
pressure, until the solution A is used for coating. The pot life of
the solution A under the sealed condition is determined by visual
observation. The solution is very stable as there are no change in
viscosity and no precipitation of solid matters after 10 days.
[0223] Preparation and Evaluation of Nonlinear-Optical Material
(Cross-Linked Cured Film C)
[0224] Subsequently, cross-linked cured film C (concentration of
the nonlinear-optically active compound backbone: about 70% by
mass), a nonlinear-optical material according to the invention, is
prepared using the stock solution C in the similar manner to
Example 1, and the film characteristics, nonlinear-optical
characteristics, and the like are evaluated in the similar manner
to Example 1.
[0225] The evaluation results thus obtained are summarized in Table
1.
Example 4
[0226] Preparation of Stock Solution D
[0227] To a solution wherein the composition used in Example 1 is
mixed and dissolved well, 0.06 part by mass of concentrated
hydrochloric acid is added as a homogeneous catalyst replacing the
solid catalyst used in Example 1. The resulting mixture is stirred
well, to give stock solution D.
[0228] Preparation and Evaluation of Nonlinear-Optical Material
(Cross-Linked Cured Film D)
[0229] Subsequently, cross-linked cured film D (concentration of
the nonlinear-optically active compound backbone: about 60% by
mass), a nonlinear-optical material according to the invention, is
prepared using the stock solution D in the similar manner to
Example 1, and the film characteristics, nonlinear-optical
characteristics, and the like are evaluated in the similar manner
to Example 1. The stock solution D should be coated immediately
after preparation, as hydrolysis and dehydration condensation
reactions proceed rapidly in the solution soon after addition of
concentrated hydrochloric acid.
[0230] The evaluation results thus obtained are summarized in Table
1.
Comparative Example 1
[0231] Preparation of Stock Solution E
[0232] To a solution wherein the composition below is mixed and
dissolved well, 0.6 part by mass of an ion exchange resin
(AMBERLYST.RTM. 15E, manufactured by Rohm and Haas Company) is
added as a solid catalyst. The slurry is stirred and reacted at
room temperature for one hour and filtered through a membrane
filter to remove the ion exchange resin. To the solution, 0.06 part
by mass of aluminum trisacetylacetonate and 0.06 part by mass of
acetylacetone are added respectively as a heat-curing catalyst and
a curing inhibitor, to give a stock solution E for production of
nonlinear-optical materials.
[0233] Nonlinear-optically active organic compound having a
hydrolysable silyl groups represented by Structural Formula (4-1):
1.5 parts by mass
[0234] Matrix-forming compound having two hydrolysable silyl groups
represented by the Structural Formula (3-2): 0.5 part by mass
[0235] Distilled water: 1.5 parts by mass
[0236] Methanol: 6 parts by mass
[0237] Tetrahydrofuran: 18 parts by mass 17
[0238] The stock solution E is immediately transferred into a
sealed container and stored at room temperature and atmospheric
pressure, until the solution E is used for coating. The pot life of
the solution A under the sealed condition is determined by visual
observation. The solution is very stable as there are no change in
viscosity and no precipitation of solid matters after 10 days.
[0239] Preparation and Evaluation of Nonlinear-Optical Material
(Cross-Linked Cured Film E)
[0240] Subsequently, cross-linked cured film E (concentration of
the nonlinear-optically active compound backbone: about 60% by
mass), a nonlinear-optical material according to the invention, is
prepared using the stock solution E in the similar manner to
Example 1, and the film characteristics, nonlinear-optical
characteristics, and the like are evaluated in the similar manner
to Example 1.
[0241] The evaluation results above are summarized in Table 1.
Comparative Example 2
[0242] A solution of 25 parts by mass of the aforementioned typical
nonlinear-optically active organic compound, Disperse Red 1 (DR1,
the structure being shown below) and 75 parts by mass of polymethyl
methacrylate functioning as the polymer binder dissolved in 600
part by mass of cyclopentanone, is coated by the spin-coating
method onto the glass substrate surface coated with ITO used in
Example 1 and dried at 100.degree. C. for 1 hour, to give a
nonlinear-optical material (concentration of the
nonlinear-optically active compound: about 25% by mass) having a
film thickness of 0.5 .mu.m. 18
[0243] The film characteristics, nonlinear-optical characteristics,
and the like of this nonlinear-optical material are evaluated in
the similar manner to Example 1. This nonlinear-optical material is
not heated for curing by cross-linking during the poling, as it is
a thermoplastic system.
[0244] The evaluation results thus obtained are summarized in Table
1.
Comparative Example 3
[0245] A solution of 55 parts by mass of DR1 and 45 parts by mass
of polymethyl methacrylate in 600 parts by mass of cyclopentanone
is coated onto the glass substrate surface coated with ITO used in
Example 1 by the spin-coating method and dried at 100.degree. C.
for one hour. There is observed precipitation of DR1 microcrystals
over the entire surface, prohibiting preparation of a clear
film.
1 TABLE 1 Stability of Stability of Nonlinear-optical
nonlinear-optical Pot life Coatability orientation characteristics
characteristics Example 1 A A A A A Example 2 A A B B B Example 3 A
A A A A Example 4 C B A A A Comparative A A A C A Example 1
Comparative A A C C C Example 2 Comparative A C -- -- -- Example
3
[0246] The evaluation items shown in Table 1 are classified
respectively according to the following criteria.
[0247] Pot Life
[0248] A: Pot life of a week or more.
[0249] B: Pot life of less than one week.
[0250] C: Pot life of less than one hour.
[0251] (The pot life means a period of time wherein the stock
solution is usable without increase in liquid viscosity or
precipitation of solid matters.)
[0252] Coatability
[0253] A: No defects such as crack, phase separation, and film
peeling detectable by visual observation.
[0254] B: Some defects slightly detectable by visual
observation.
[0255] C: Some defects detectable over the entire surface by visual
observation.
[0256] Stability of Orientation
[0257] A: Decrease in order parameter of less than 10% after
storage in a dark place for 10 days.
[0258] B: decrease in order parameter of 10% or more after storage
in a dark place for 10 days.
[0259] Nonlinear-Optical Characteristics
[0260] When the light intensity of the second harmonics generated
in Example 1 is designated as level A, the nonlinear-optical
characteristics are judged as follows:
[0261] A: Light intensity of the second harmonics generated is
equivalent or more than that generated in Example 1.
[0262] B: Light intensity of the second harmonics generated is half
or more of that generated in Example 1.
[0263] C: Light intensity of the second harmonics generated is less
than half of that generated in Example 1.
[0264] Stability of Nonlinear-Optical Characteristics (Oriented
State)
[0265] A: The light intensity of the second harmonics generated
after storage at 150.degree. C. for one hour is equivalent to that
before storage.
[0266] B: The light intensity of the second harmonics generated
after storage at 150.degree. C. for one hour is half or more of
that before storage.
[0267] C: The light intensity of the second harmonics generated
after storage at 150.degree. C. for one hour is less than half of
that before storage.
Example 5
[0268] A Mach-Zehnder optical modulator (nonlinear-optical device)
having a reverse-ridge waveguide structure set forth in FIG. 4 is
prepared, using a nonlinear-optical material according to the
invention.
[0269] First, a lower cladding layer 4 having a thickness of 5
.mu.m is formed by using a UV-curing epoxy resin manufactured by
Nagase ChemteX. Two grooves (waveguide channels) of 4 .mu.m in
width and 1 .mu.m in depth are formed on the surface of this lower
cladding layer 4 by reactive ion etching.
[0270] A core layer 3 having a thickness of 4 .mu.m is formed on
the surface of this lower cladding layer 4, using the stock
solution C used in Example 3, and the core layer 3 is subjected,
immediately after coating, to the heat curing and electric-field
poling treatments in the similar manner to Example 3. An upper
cladding layer 2 having a thickness of 3 .mu.m is then formed by
using a toluene solution of a polycyclic olefin resin manufactured
by JSR. The interaction length is 2 cm.
[0271] After connecting a top electrode 1, the electro-optical
characteristics of the optical modulator obtained are evaluated by
measuring modulation of the output light intensity from an input
laser beam at 1,318 nm while applying a drive voltage to the top
electrode 1. The modulator is driven in the single-drive mode. As a
result, an electro-optical effect that the intensity of output
light is modulated according to the drive voltage applied is
observed. The half-wave voltage, a measure of modulation capacity,
is as high as about 5 V, indicating that the optical modulator has
an excellent electro-optical characteristics. After storage at
150.degree. C. for one hour, the optical modulation characteristics
of the same optical modulator are evaluated. The optical modulator
retained the same characteristics as those before storage,
indicating that the optical modulator has extremely high thermal
stability.
Comparative Example 4
[0272] An optical modulator (nonlinear-optical device) is prepared
in a similar manner to Example 5, except that the core layer 3 is
formed by using the stock solution E of Comparative Example 1
replacing the stock solution C of Example 5, and evaluated in the
similar manner to Example 5.
[0273] As a result, an electro-optical effect that the intensity of
output light is modulated according to the drive voltage applied is
observed in a similar manner to Example 5. However, the half-wave
voltage is very high at about 50 V, indicating that the optical
modulator is significantly lower in electro-optical characteristics
compared to the optical modulator of Example 5.
Comparative Example 5
[0274] An optical modulator (nonlinear-optical device) is prepared
in the similar manner to Example 5, except that the core layer 3 is
formed by using the stock solution E of Comparative Example 2
replacing the stock solution C of Example 5, and evaluated in the
similar manner to Example 5.
[0275] As a result, an electro-optical effect that the intensity of
output light is modulated according to the drive voltage applied is
observed in a similar manner to Example 5. However, the half-wave
voltage is very high at not less than 100 V, indicating that the
optical modulator is significantly lower in electro-optical
characteristics compared to the optical modulator of Example 5. In
addition, when the optical modulation characteristics are evaluated
once more after storage at 150.degree. C. for one hour, most of the
optical modulation characteristics have disappeared, indicating
that the optical modulator is significantly lower in thermal
stability of electro-optical characteristics, compared to the
optical modulator of Example 5.
* * * * *